Fast switching of forward link in wireless system

ABSTRACT

A technique for distributing channel allocation information in a demand access communication system. Multiple access codes are used that have a defined code repeat period or code epoch. For each such epoch duration, a schedule of assignment of traffic channels to active terminals for each epoch is determined. For each terminal designated as active during the epoch, a list of active channels for such terminal unit is assigned. Prior to the start of each epoch, a channel set up message is sent on one of the forward link channels, such as a paging channel, indicating the lists of active channels for epochs of the associated traffic channel(s) that are to follow.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/533,708 filed Jun. 26, 2012, which is a continuation of U.S. patentapplication Ser. No. 11/978,309, filed Oct. 29, 2007, now U.S. Pat. No.8,218,562, issued Jul. 10, 2012, and is a continuation of U.S. patentapplication Ser. No. 11/053,092, filed Feb. 7, 2005, now U.S. Pat. No.7,289,469, issued Oct. 30, 2007, and is a continuation of U.S. patentapplication Ser. No. 09/847,860 filed May 2, 2001, now U.S. Pat. No.6,853,646, issued Feb. 8, 2005, which are incorporated by reference asif fully set forth.

BACKGROUND

This invention relates generally to wireless communication systems, andmore particularly to a technique for high speed re-allocation of codedradio channel resources that are shared among a number of users.

Demand for wireless communications equipment and services continues togrow at an unprecedented rate throughout the world. Increasingly, suchsystems are commonly relied upon to provide voice and datacommunications to a growing sector of the public. While these systemsoriginally depended upon analog signaling technology, there isessentially unanimous agreement that future systems will be based onvarious types of digital signal coding schemes.

The typical wireless communication system is a point to multi-point typesystem in which a central base station communicates with a number ofremote units located within a local geographic area of coverage known asa cell. This system provides for duplex communication such that signalsmay be sent in both a forward direction (from the base station to theremote unit) as well as in a reverse direction (from the mobile remoteunit back to the base station). In order to support communicationbetween the remote unit and networks such as Public Switched TelephoneNetwork (PSTN), or data networks such as the Internet, the wirelesssystem must also provide for various other logical components andfunctional entities.

Consider the Code Division Multiple Access (CDMA) and Time DivisionMultiple Access (TDMA) digital systems presently in widespread use. Eachof these systems provides for certain logical types of the radiochannels that make up the forward link and reverse link. In particular,the forward link channels often include a pilot channel, pagingchannels, and multiple forward traffic channels. The traffic channelsare used to carry the payload data between the base station and themobile unit. A pilot channel is also typically required to allow theremote unit to maintain synchronization with the base station. Thepaging channels provide a mechanism for the base station to inform theremote unit of control information, such as the assignment of particularforward traffic channels to particular connections and/or subscriberunits.

Likewise, an access channel is provided in the reverse direction inaddition to reverse traffic channels. The access channels allow theremote units to communicate control information with the base station,such as to send messages indicating the need to allocate or deallocateconnections as required.

Unfortunately, users both compete for access to the available radiospectrum, while at the same time demanding data transmission rates thatare as fast as possible. This situation is most acute in the forwardlink direction, where users of remote computing equipment are performingtasks such as accessing the World Wide Web. The forward link directiontypically represents the direction of greatest data transfer, e.g., inconnection with the downloading of web pages and files from remoteservers.

It is critical therefore, for the channel allocation algorithms, andradio channel protocols to be as efficient as possible. As demand foraccess to the available radio spectrum changes almost instantly among alarge group of users of such a wireless data network, maximum efficiencyrequires the ability to rapidly reassign channels. However, traditionalwireless system architectures and protocols, such as those used incellular telephone systems, were not designed with rapid channelchanging in mind. They typically keep an end-to-end connection open forthe duration of a session or call, and reassign channels only as amobile unit moves from cell to cell.

Thus, these architectures use a protocol whereby a paging channel isused to send a message to a remote unit when a channel change is needed.The message is then received and acknowledged by the remote unitreturning a channel acknowledgment to the central base station.

In an ideal wireless data environment, the channel assignments should bechangeable many times during the duration of a given session, asinstantaneous demand for access to the available radio bandwidth ebbsand flows, e.g., as individual users make requests to download web pagesand files.

SUMMARY

The present invention is a technique adapted for allocating channels ina demand access system. In a preferred embodiment, the invention isimplemented in a system which supports Code Division Multiple Access(CDMA) communication among a group of terminals wherein the terminalsshare access to a predetermined number of CDMA traffic channels.

A method according, to the invention involves first assigning to thegroup of terminals a multiple access code having a code epoch repeatduration. In a preferred embodiment, the code epoch duration shouldremain constant, even if the underlying data rates change due to errorcoding requirements.

For each such epoch duration, a central controller such as located at abase station, determines a schedule of assignment of traffic channels toactive terminals for each epoch. For each terminal designated as activeduring the epoch, an active terminal unit identifier is assigned. Theactive terminal unit identifier should be as short as possible to allowthe channel assignment message to be as short as possible. Thus, theactive terminal unit identifier does not have to uniquely identify theremote terminal among all possible terminals in the system, and onlyneeds to uniquely identify the terminal among other active terminalsbeing serviced by the particular base station.

For each terminal designated as active during the epoch, the basestation assigns a list of active channels for such terminal unit. Priorto the start of each epoch, a channel set up message is sent on theforward link, such as a paging channel. The channel set up messageindicates the terminal unit identifiers and the lists of active channelsfor such epoch which is to follow.

At the remote terminal unit, upon receiving a paging channel message, anactive terminal identifier is determined from each paging channelmessage and compared to a previously assigned terminal identifier. On apredetermined subsequent epoch, the indicated active traffic channel, asindicated from the list of active traffic channels indicated by areceived paging channel message, are then processed.

The paging channel messages may be time slotted so that multiple activeremote terminals can be serviced by a shared paging channel.

In a preferred embodiment, the list of active channels for each epochmay be indicated by a pipe group identifier, with each pipe groupidentifier effectively indicating a group of active channels that areassigned together.

The paging channel messages should be sent at a time advancedsufficiently to permit code setup in a receiver prior to the epochcontaining the associated traffic channel data.

The paging channel set up message may also include other information,such as to indicate a coding rate for the associated traffic channels, aspecification for which portions of the payload are intended forparticular terminals, or a reverse link channel identifier for theremote terminal to use for transmissions back to the base station duringthe associated epoch. Still other information, such as messages forcontrol processors in the terminals, can be carried.

Allocation of forward link channels in this fashion affords precise andrapid control over which terminals are assigned to specific trafficchannels, on an epoch-by-epoch basis. This arrangement, therefore,affords great flexibility in capacity management, allowing channelallocation decisions to be made on a very fine time scale. For example,channel switch decisions can thus be made rapidly, in response tochanges in radio propagation conditions, such as fading conditions.

BRIEF DESCRIPTION OF THE DRAWING(S)

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a block diagram of a wireless data communication system inwhich the present invention may be implemented.

FIG. 2 is a more detailed view of a signal encoder used in the system.

FIG. 3 illustrates the timing of paging channel epoch with respect to acorresponding traffic channel epoch.

FIG. 4 illustrates the format of a portion of paging channel message.

FIG. 5 is a pipe configuration table maintained at a base stationprocessor.

FIG. 6 is a pipe schedule.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a wireless communication system 10 thatmakes use of a code channel assignment scheme and message protocolwhere, prior to the start of each code epoch, a paging channel messageis sent that indicates terminal unit identifiers and active channels forsuch epoch.

In the following detailed description of a preferred embodiment, thecommunication system 10 is described such that the shared channelresource is a wireless or radio channel. However, it should beunderstood that the techniques described here can be applied to allowshared access to other types of media such as telephone connections,computer network connections, cable connections, and other physicalmedia to which access is granted on a demand driven basis.

The communication system 10 includes a number of Personal Computer (PC)devices 12-1, 12-2, . . . 12-h, . . . 12-l, corresponding remote, mobileSubscriber Access Units (SAUs) 14-1, 14-2, . . . 14-h, . . . 14-l, andassociated antennas 16-1, 16-2, . . . 16-h, . . . 16-l. Centrallylocated equipment includes a base station antenna 18, and a Base StationProcessor (BSP) 20. The BSP 20 provides connections to and from anInternet gateway 22, which in turn provides access to a data networksuch as the Internet 24, and network file server 30 connected to thenetwork 22.

The system 10 is a demand access, point to multi-point wirelesscommunication system such that the PCs 12 may transmit data to andreceive data from network server 30 through bi-directional wirelessconnections implemented over forward links 40 and reverse links 50. Itshould be understood that in a point to multi-point multiple accesswireless communication system 10 as shown, a given base stationprocessor 20 supports communication with a number of different activesubscriber access units 14 in a manner which is similar to a cellulartelephone communication network.

The PCs 12 may typically be laptop computers 12-l, handheld units 12-h,Internet-enabled cellular telephones or Personal Digital Assistant(PDA)-type computers. The PCs 12 are each connected to a respective SAU14 through a suitable wired connection such as an Ethernet-typeconnection.

An SAU 14 permits its associated PC 12 to be connected to the networkfile server 30 through the BSP 20, gateway 22 and network 24. In thereverse link direction, that is, for data traffic traveling from the PC12 towards the server 30, the PC 12 provides an Internet Protocol (IP)level packet to the SAU 14. The SAU 14 then encapsulates the wiredframing (i.e., Ethernet framing) with appropriate wireless connectionframing and encoding. The appropriately formatted wireless data packetthen travels over one of the radio channels that comprise the reverselink 50 through the antennas 16 and 18. At the central base stationlocation, the BSP 20 then extracts the radio link framing, reformattingthe packet in IP form and forwards it through the Internet gateway 22.The packet is then routed through any number and/or any type of TCP/IPnetworks, such as the Internet 24, to its ultimate destination, such asthe network file server 30.

Data may also be transmitted from the network file server 30 to the PCs12 in a forward link 40 direction. In this instance, an InternetProtocol (IP) packet originating, at the file server 30 travels throughthe Internet 24 through the Internet gateway 22 arriving at the BSP 20.Appropriate wireless protocol framing and encoding is then added to theIP packet. The packet then travels through the antenna 18 and 16 to theintended receiver SAU 14. The receiving SAU 14 decodes the wirelesspacket formatting, and forwards the packet to the intended PC 12 whichperforms the IP layer processing.

Each SAU 14 typically has multiple channel signal processors 100 withinit to perform the required wireless signal processing and protocolframing functions. This permits each SAU to receive multiple trafficchannels 42 and paging channels 41 at the same time. Each SAU also has aMicro Controller Unit (MCU) 101 that coordinates the operation of thechannel signal processors 100 and performs other functions, such ashigher layer protocol processing.

A given PC 12 and the file server 30 can therefore be viewed as the endpoints of a duplex connection at the IP level. Once a connection isestablished, a user at the PC 12 may therefore transmit data to andreceive data from the file server 30.

The reverse link 50 actually consists of a number of different types oflogical and/or physical radio channels including an access channel 51,multiple traffic channels 52-1, . . . 52-t, and a maintenance channel53. The reverse link access channel 51 is used by the SAUs 40 to sendmessages to the BSP 20 to request that traffic channels be granted tothem. The assigned traffic channels 52 then carry payload data from theSAU 14 to the BSP 20. It should be understood that a given IP layerconnection may actually have more than one traffic channel 52 assignedto it. In addition, a maintenance channel 53 may carry information suchas synchronization and power control messages to further supporttransmission of information over the reverse link 50.

Similarly, the forward link 40 typically includes a paging channel 41,traffic channels 42-1 . . . 42-t, and maintenance channel 43. The pagingchannel 41 is used by the BSP 20 to not only inform the SAU 14 thatforward link traffic channels 52 have been allocated to it, but also toinform the SAU 14 of allocated traffic channels 52 in the reverse linkdirection. Traffic channels 42-1 . . . 42-t on the forward link 40 arethen used to carry payload data information from the BSP 20 to the SAUs14. Additionally, maintenance channels 43 carry synchronization andpower control information on the forward link 40 from the base stationprocessor 20 to the SAUs 14. It should be understood that there aretypically many more traffic channels 41 than paging channels 41 ormaintenance channels 43.

In the preferred embodiment, the logical channels 41-43 and 51-53 aredefined by assigning, each channel a unique channelization code. Thesystem 10 is therefore a so-called Code Division Multiple Access (CDMA)system in which multiple logical channels assigned to unique codes mayuse the same radio frequency (RF) channel. The logical or codes channelsmay also be further divided or assigned among multiple active SAUs 14.Additional information as to one possible way to implement the variouschannels 41, 42, 43, 51, 52, and 53 is provided in Patent CooperationTreaty Application No. WO99/63682 entitled “Fast Acquisition Of TrafficChannels For A Highly Variable Data Rate,” assigned to TantivyCommunications, Inc., and published on Dec. 9, 1999.

Turning attention to FIG. 2 there is shown a generalized block diagramof a transmit signal encoding process used by the channel signalprocessor 100. The illustrated sequence of signal processing operationsis performed to format, encode, and modulate at least the respectiveforward link 40 logical channels within the Base Station Processor (BSP)20. Although the invention is described herein as being applied to theforward link 40, it should be understood that in other implementationsit is possible for the invention to be applied on the reverse link 50,in which case the receiver is implemented in the BSP 20 and thetransmitters are the SAUs 14.

In any event, a channel signal processor 100 includes a block formatter110, Forward Error Correction (FEC) or block coder 120, channel coder140 and radio frequency (RF) modulator 150. It should be understood thata corresponding receiver (not shown) performs the inverse functions ofthe corresponding portions of the transmitter signal processor 100. Insuch an instance, an RF demodulator performs the inverse radio frequencyto modulation process, a channel decoder decodes the channel codesreversing the operation of the channel coder 140, and a block decodeprocess also undoes the block encoder 120 and block formatter 110.

Before discussing the details of the block formatter 110 in more detail,it is instructed to consider the operation of the block encoder 120which formats input data bits according to an error coding process. Inparticular, consider an example situation in the use of a turbo productcode which is to encode data at the rate of ¼. Because the code is a ¼rate code, the matrix encoding space consists of a matrix which is fourtimes the size of the input data matrix space. Thus, a group of 1024input bits are encoded as 4096 output bits by the block encoder 120.Thus, in the case of a ¼ rate code, three times as many parity bits asdata bits are calculated and created.

However, in the preferred embodiment, the system provides for selectionof a different rate turbo product code depending upon channelconditions, demand for use and other factors. Thus, at any given time,the selected block encoder 120 may be encoding the input data at a ⅔rate, a ½ rate, or a ¼ rate.

Now more particularly, an input data frame, which may for example, be aTCP/IP frame, is first fed to a block formatter 110. The block formatter110 packages input payload data into conveniently sized groups referredto as blocks. The size of these pre-encoded frames will vary dependingupon the particular forward error correction (FEC) coding schemeselected at any given time by the block encoder 120. What is importantis that the combination of the block formatter 110 and block encoder 120produce a fixed number of output FEC symbols in each given transmittedblock.

Thus, when the ¼ rate is selected by the block encoder 120, a ¼ rateblock format 110 function is selected which groups incoming bits intopre-encoded FEC groups of 1024 bits, producing the desired 4096 outputsymbols. Similarly, when the ½ rate block encoder 120 is enabled, theblock formatter 110 groups incoming bits into pre-encoded sets of 2048bits. When the ⅔ rate block encoder 110 is enabled, the block formattergroups 2730 input bits together.

The block formatter 110 and block encoder 120, working together,therefore ensure that a fixed block size of 4096 bits is fed to thechannel coder 140. This in turn becomes important, since it permits theoutput of the channel coder 140 to include a known number of transmittedsymbols per code epoch length. Thus, a fixed number of FEC symbols ismaintained per transmitted block, independent of the FEC coding ratesand power levels. This allows a different FEC rate or even a differentFEC code to be assigned to each user channel, depending upon channelconditions, without changing the effective transmitted power levels.

The channel coder 140 accepts the block encoded data as a digital inputsignal. In the illustrated preferred embodiment, the channel coderincludes a quadrature phase shifter 141, a short code generator 141, afirst pair of quadrature modulators 142-i and 142-q, a long codegenerator 143, and a second pair of quadrature modulators 144-i and144-q.

The quadrature phase shifter 141 accepts the input digital data signaland provides in-phase (i) and quadrature (q) signal paths.

The short code generator 141 is a 2¹⁵ length repeating code generator.It may be any suitable channel spreading sequence such as a pseudonoise(PN) sequence. The short code is fed to both the in-phase 142-i andquadrature 142-q modulators to spectrum-spread the respective signalpaths.

In the preferred embodiment, the resulting output coded signal rate isdesired to be 1.2288 Mega samples per second (Msps), to be compatiblewith legacy digital CDMA cellular systems. With a fixed block size of4096 input bits and a short code length of 2¹⁵, this means that the PNspreading code epoch, or its repeat interval, is therefore 26milliseconds (ms). In a preferred embodiment, the channel codes are atype of augmented PN code sequence which repeats at a code length ofexactly 2¹⁵. One such coding scheme is described in U.S. patentapplication Ser. No. 09/255,156, filed Feb. 23, 1999, entitled “Methodand Apparatus for Creating Non-Interfering Signals Using Non-OrthogonalTechniques”, assigned to Tantivy Communications, Inc.

The long code generator 143 is a 2⁴² length code generator. This code isused to uniquely identify the respective paging channel 41, trafficchannel 42, or maintenance 43. The long code may be a pseudonoise (PN),Walsh or other code sufficient to produce the CDMA channel signals 41,42, or 43. Typically, the same long code is used for each channel, butwith a unique code phase offset being used by each such channel. As withthe short code modulation process, the long code is fed to an in-phasemodulator 144-i and quadrature modulator 144-q.

In certain instances, the long code generator 143 may not be used or maybe in a different position in the process. For example, where it isdesired that a particular traffic channel 42 is to be shared amongmultiple SAUs 14 during a given epoch, the long code generator 143typically would not be used. Alternatively, in such an instance, thelong code generator 143 could be located before the FEC block coder 120.

The RF modulator 150 accepts the digitally encoded signals, convertsthem to digital signals, and up-converts their carrier frequency to adesired radio frequency carrier, as is well known in the art.

Now turning, attention to FIG. 3 the present invention can be understoodmore precisely. Illustrated there is an example of a series ofsuccessive epochs 180-1, 180-2, . . . that make up the paging channel41. The idea with the present invention is to have the paging channeloperate simultaneously with the traffic channel, so that channelassignment information can be continuously sent to the SAUs 14. Thepaging channel data is formatted into epochs 180-1, 180-2, . . . , asdictated by the channel coding in use. As explained above, for thedesired 4096 block size, 2¹⁵ channel code length, and 1.2288 Msps outputdata rate, the epoch duration is 26 ms.

Each epoch in the paging channel is time slotted, such that a time slotis devoted to one of the active or standby SAUs being serviced by theBSP 20. The time slots carry enough information to permit each potentialreceiving SAU 14 to determine unique code assignments for respectiveepochs 190-1, 190-2, . . . of the traffic channels 42. The timing of thetraffic channel epochs 190 is therefore delayed with respect to theassociated paging channel epoch 180. Advancing the channel switchinginformation relative to the delivery of the payload information in thetraffic channel provides time for decoding and reconfiguration of thereceiving SAUs 14. The amount of this time delay depends upon the amountof time needed to setup the code demodulators in the respectivereceiver. In a preferred embodiment, this time delay is equal toapproximately one-half the epoch duration, or 13 ms.

It has been found to be advantageous to separate the broadcast of codechannel information into the dedicated paging channel 41 rather thanattempt to include it with the encoded traffic channel 42 payload data.This is because the traffic channels 42 are ideally power controlledsuch that the traffic channels 42 a associated with one of the SAUs 14 amay not necessarily be transmitted at the same power level as thetraffic channels 42 b assigned to another one of the SAUs 14 b. Forexample, a signal transmission intended for an SAU 14 a which is locatedcloser to the BSP 20, typically does not need to use as much signalpower as a transmission intended for an SAU 14 b which is locatedfarther away from the BSP 20. However, the power level of the channelthat carries the channel switching, information should be sufficientlyhigh at all times so that all active and standby SAUs 14 (e.g., all ofthose which are not in an idle or off mode) can reliably obtain theirchannel assignment information.

Turning attention to FIG. 4, the format of the paging channel and thechannel setup information contained therein will now be described ingreater detail. An epoch 180-1 of the paging channel is devoted to abroadcasting in a format that contains a series of time slots 200-1,200-2, . . . , 200-f. The number, f, of time slots 200 depends upon themaximum number of SAUs 14 that are expected to be in an active mode(e.g., presently in the process of receiving, data) or an idle mode(e.g., having active higher layer connections or sessions but notpresently receiving data).

Each time slot 200 contains a Digital Signal Processor (DSP) data field210 and an MCU messaging field 212.

The DSP data field 210 includes in turn, an active SAU identifier (SAUID) 214, a pipe number 216, a coding rate 218, a reverse link number220, and one or more additional message segments 222-1, 222-2, . . . ,222-m.

For each traffic channel epoch 190 duration, a central controller suchas located at the BSP 20, determines a schedule of assignment of trafficchannels 42 to active and standby SAUs 14 terminals for that epoch. Foreach SAU 14 designated as active during the epoch, an active SAU ID isassigned. The active SAU ID 214 can be as short as possible to allow thetime slots 200 in the paging channel to be as short as possible. Thus,the active SAU ID 214 does not have to be a serial number that issufficiently long to uniquely identify the specific SAU 14 among allpossible devices in the system 10. It only needs to uniquely identifythe SAU 14 among other active or standby SAUs 14 being serviced by theparticular BSP 20 at a given time

The SAU ID 214 can be assigned to the SAU 14 during an initialauthentication process. However, if the epoch 26 duration and number oftime slots 200 permits, this SAU ID can be more in the nature of adevice serial number.

Also during, an authentication procedure, or at some other time prior toexpected reception of the paging channel messages, each SAU 14 may begiven certain information such as pipe configurations, which will beexplained in further detail below.

In any event, for each SAU 14 designated as active or standby duringeach epoch 26, the BSP 20 assigns a list of active channels for suchterminal unit. Then, prior to the start of each epoch, information inthe form of a pipe identifier 216 is sent in the associated time slots200 in paging channel. The pipe identifier indicates a group of codechannels for which the specific SAU 14 is to receive traffic channeldata in the next following traffic channel epoch 190.

The BSP 20 may therefore maintain a couple of tables such as are shownin FIGS. 5 and 6. FIG. 5 illustrates a pipe configuration table 250. Thenotion of a “pipe” herein is the assignment of one or more code channelstogether in a group. Thus, for example, pipe 1 is a shorthand notationreferring to code channels 1 and 2; pipe 2 is a notation indicating codechannels 1, 2, 3, and 4; and so on.

A pipe schedule 252 is also maintained in the BSP 20, such as is shownin FIG. 6. The pipe schedule 252 is a master plan for how the availablepipes are to be assigned to specific active or standby SAUs 14 for eachepoch 190. The exact manner of deciding which channels and how manychannels to assign to specific SAUs is not the concern of the presentinvention. It suffices here to say that this depends upon how many SAUsare active, how much data has been queued for transmission to a specificSAU 14, how far away each SAU 14is from the BSP 20 and hence how much ofa drain is it on the available power link budget, whether the system 10supports any notion of tiered service, where certain users have priorityover other users, and other considerations.

The pipe notation permits the channel setup information in each timeslot 200 to be as concise as possible, while allowing rapid allocationand deallocation of multiple code channels for each epoch as needed.

At the SAU 14, upon receiving the paging, channel message, the activeSAU ID 214 is read for each time slot. The SAU ID is then compared toany previously assigned to that particular SAU 14. If the SAU ID isrecognized as one of its own, the SAU 14 will then continue to processthe remainder of the information in the time slot 200, to determine thepipe identifier 216, code rate 218, reverse link 220 and control messageinformation 222 that pertains to its next traffic channel epoch 190.

On a predetermined subsequent epoch 190 of the traffic channel, the SAU14 may then be set up to receive its assigned channels, as indicatedfrom the pipe identifier. Have already received the pipe configurationinformation during authentication, each SAU 14 can then determine a listof channels to which it should be listening during the next trafficchannel epoch.

As explained above, the information in the paging channel time slots 200should be sent at a time advanced sufficiently to permit setup of therequired number of code channel receivers in each SAU 14.

The paging channel set up message may also include other information,such as to indicate a coding rate 218 for the associated trafficchannels. This permits implementation of the variable rate FEC codes asmentioned above in connection with FIG. 2.

Also, additional information such as a reverse link channel identifier220 can be included in the paging channel slots 200. This can indicate achannel number for the SAU 14 to use for reverse link transmissions backto the Base Station Processor 20, such as to carry physical layer replymessages associated with the same epoch. Such messages may include, forexample, physical layer acknowledgment (ACI) messages and the like.

The MCU messaging field 212 can be used to carry messages from the BSP20 to the MCUs 101. This can further expedite the transmission of shortmessages on the forward link that are sent frequently. For example, theMCU messaging field 212 may be used to carry link layer acknowledgementmessages.

Other information can be carried in control segment portions 222associated with each paging channel slot 200, if needed. The controlsegment portions 222 can be used to support the sharing of a singletraffic channel 42 among multiple SAUs 14. For example, the segment 222information can specify how the data carried in the epoch 190 associatedwith the paging channel slot 200 is to be shared among the multiple SAUs14. A first control segment (seg1) may indicate a starting bit positionfor a first SAU sharing the associated traffic channel 42, (seg2) toindicate a starting bit position for a second SAU 14 sharing the trafficchannel 42, and so on.

What is claimed is:
 1. A subscriber unit comprising: a memory; aprocessor coupled with the memory, the processor to process controlinformation received on a shared channel; wherein the controlinformation is received in a time slot of the shared channel; whereinthe subscriber unit is to receive from a base station, a list of activechannels for the respective subscriber unit as assigned by the basestation, based on the respective subscriber unit having been designatedas active or standby during an epoch by the base station; wherein thecontrol information includes an indication of code channels assigned tothe subscriber unit; wherein the subscriber unit is to determine a listof channels to which to listen during a subsequent traffic epoch;wherein the subscriber unit is to further receive, at a predeterminedtime interval and after reception of the control information, the codechannels indicated by the control information; and wherein thesubscriber unit is to recover packet data from the control channelsindicated by the control information.
 2. The subscriber unit of claim 1wherein the code channels are received in a time interval including aninteger number of slots.
 3. The subscriber unit of claim 1 wherein thepredetermined time interval is an integer number of slots.
 4. Thesubscriber unit of claim 1 wherein the code channels are dynamicallyassigned on a time interval basis.
 5. The subscriber unit of claim 1wherein the processor is further configured to receive a terminalidentifier and the processor is further configured to determine whetherthe control information is for the subscriber unit based on the terminalidentifier.
 6. The subscriber unit of claim 1 wherein the controlinformation includes one or more of data rate information, reverse linkchannel identifier, and a coding rate.
 7. A method comprising:processing, by a subscriber unit, control information received on ashared channel; wherein the control information is received in a timeslot of the shared channel; wherein the subscriber unit is to receivefrom a base station, a list of active channels for the respectivesubscriber unit as assigned by the base station, based on the respectivesubscriber unit having been designated as active or standby during anepoch by the base station; wherein the control information includes anindication of code channels assigned to the subscriber unit; wherein thesubscriber unit is to determine a list of channels to which to listenduring a subsequent traffic epoch; wherein the subscriber unit is tofurther receive, at a predetermined time interval and after reception ofthe control information, the code channels indicated by the controlinformation; and wherein the subscriber unit is to recover packet datafrom the control channels indicated by the control information.
 8. Themethod of claim 7 wherein the code channels are received in a timeinterval including an integer number of slots.
 9. The method of claim 7wherein the predetermined time interval is an integer number of slots.10. The method of claim 7 wherein the code channels are dynamicallyassigned on a time interval basis.
 11. The method of claim 7 furthercomprising receiving a terminal identifier and determining whether thecontrol information is for the subscriber unit based on the terminalidentifier.
 12. The method of claim 7 wherein the control informationincludes one or more of data rate information, reverse link channelidentifier, and a coding rate.
 13. A base station comprising: a memory;a processor coupled with the memory, the processor to send controlinformation to a subscriber unit on a shared channel; wherein the basestation is to send to the subscriber unit, a list of active channels forthe respective subscriber unit as assigned by the base station, based onthe respective subscriber unit having been designated as active orstandby during an epoch by the base station; wherein the controlinformation is sent in a time slot of the shared channel; wherein thecontrol information includes an indication of code channels assigned tothe subscriber unit; and wherein the base station is to transmit packetdata on the code channels indicated by the control information at apredetermined time interval after transmission of the controlinformation.
 14. The base station of claim 13 wherein the code channelsare transmitted in a time interval including an integer number of slots.15. The base station of claim 13 wherein the predetermined time intervalis an integer number of slots.
 16. The base station of claim 13 whereinthe code channels are dynamically assigned on a time interval basis. 17.The base station of claim 13 wherein the processor is further configuredto transmit a terminal identifier to the subscriber unit for thesubscriber unit to identify the control information is intended for thesubscriber unit.
 18. The base station of claim 13 wherein the controlinformation includes one or more of data rate information, reverse linkchannel identifier, and a coding rate.